Mark fast/images/gif-loop-count.html as flaky on mac
Mark fast/images/gif-loop-count.html as flaky on mac

BUG=244276

Review URL: https://codereview.chromium.org/15864008

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@151197 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs